Which symptom might indicate joint involvement in rheumatoid arthritis?

Joint fluid with inflammatory exudate is a key indicator of joint involvement in rheumatoid arthritis. This condition is characterized by synovial inflammation, which leads to an accumulation of synovial fluid in the joint spaces. In rheumatoid arthritis, this fluid often becomes inflammatory due to the presence of immune cells and inflammatory markers, resulting in an increase in protein content compared to normal joint fluid. The presence of this inflammatory fluid can contribute to the swelling, pain, and decreased range of motion typically observed in affected joints.

Localized swelling may also occur in other joint conditions, not just rheumatoid arthritis, and does not specifically indicate the presence of inflammatory exudate. A significant increase in mobility would be counterintuitive in rheumatoid arthritis, as the disease usually results in stiffness and reduced range of motion due to pain and inflammation. Constricted blood flow to muscles is not a direct symptom of joint involvement; rather, it pertains to vascular issues and is not characteristic of rheumatoid arthritis itself. Therefore, option B stands out as the clear indicator of joint involvement in this autoimmune disorder.